Re: Recent s.s.t.c. work

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Steve Ward" <steve.ward@xxxxxxxxx>

Hi Ken,

Will you be employing your delay register on this next attempt to try
and compensate for delays?  I hope that works as expected.  Be sure to
have a camera handy to take pictures of the sparks!

Good luck, let us know how it turns out.

Steve

On 3/24/06, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>
>
> I see that my last posting on this topic was in December.  In the
> interim I've been slothful to a fault (altho happily busy for 3 of
> the weeks entertaining our Most Perfect Granddaughter, 2 1/2,
> visiting from Berlin).  But I have now gotten to the stage where I'm
> ready to put the H.V. to it once again.  I've checked the gate
> waveforms & all 4 appear OK.  Next, it's... turn up the variac &
> watch for the smoke.  It's only trepidation, accumulated from years &
> years of such practice, that keeps me from doing it today; So perhaps
> I'll first just sit & think about it for a while...
>
> Someone asked, after I reported my last failure (death of an IGBT
> brick), what might have caused it, and at the time I didn't
> know.  But while rebuilding the drivers, I discovered that I had
> positioned a wire-wrap pin, in one of the gate circuits, so that,
> when I fastened the board down above the mains capacitors, the pin
> pressed against one of the capacitor terminals--hidden from view, of
> course.  I didn't locate the source of the resultant smoke until I
> started rebuilding.
>
> As I've already reported, I utilize NPN/PNP emitter-follower
> driver-pairs for each of the 4 H-bridge IGBTs, transformer-driven,
> with the 4 transformer signals always applied (from my "pilot
> oscillator")--and now rebuilt with opto-isolators acting to gate-on
> drive to the NPNs during the spark-event times.  That way, all 4 gate
> voltages are kept at -28 or so between sparks by the continuous drive
> from the PNPs.  As before, the continuous transformer signal also
> serves to keep the + and - drive-supply electrolytics charged up.
>
> So stay tuned, so to speak--& don't be startled by smoke seen coming
> from the vicinity of California; it'll only be me once again.
>
> Ken Herrick
>
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